Recurrent Defects

John FRANKLIN • 2 December 2020
in community Air Operations

History shows that a number of accidents and high risk occurrences have been linked to recurrent defects and technical faults on aircraft components and systems. These events were the result of repetitive defects that had not been properly resolved.  If you involved in maintenance or continuing airworthiness activities, this article will highlight some examples where recurrent faults have played a role and then give you some ideas of how you can reduce the risk of this problem to the safety of operations. 

When recurrent faults remain unresolved, history shows they can lead to accidents or other high-risk occurrences. As a Continuing Airworthiness Maintenance Organisation (CAMO) there are things that you and your staff can do to manage recurrent faults effectively and to reduce the associated risks. The main points are below - we provide more detail later in the article: 

  • Correctly report and record defects in the technical log book. 
  • Monitor, analyse and investigate recurrent faults through the defect control system. 
  • Establish clear policies and coordination between the CAMO, the maintenance organisation and all personnel involved in any maintenance activity.    
  • Follow the relevant maintenance and troubleshooting procedures provided by the Type Certificate Holder (TCH).    

Examples of the Risk Posed by Recurrent Faults

Airbus A320 (PK-AXC) on 28 December 2014:

The final report KNKT. issued by the Republic of Indonesia indicated that there were 23 occurrences related with the Rudder Trim Limiter Unit (RTLU) over the previous last 12 months.  Of these, 10 were during the 30 days prior to the accident.  The rectification of the defects were incomplete, always considered “closed” and noted “no further action required” – “computer reset”.  The accident report cited unresolved repetitive faults as one of the contributing factors. 

There was no policy of recording defect handling captured by the Centralised Fault Display System (CFDS) or printed Post Flight Report (PFR) - only recorded partial reports were done.  None of the issues reported were identified as meeting the repetitive defect definition which would have triggered maintenance actions under the requirements of the Company Maintenance Manual (CMM).  Additionally the monthly reliability reports concerning the aircraft did not match the number of precursor events.

Airbus A319 (G-EZAG) on 15 September 2006

The report EW/C2006/09/04 in this serious incident revealed that the Master Minimum Equipment List (MMEL) allowed dispatch with a main generator inoperative without consideration of any previous history of electrical system faults on the aircraft.  Moreover the reporting identified that inadequate measures were taken for identifying Generator Control Units repeatedly rejected from service due to repetition of the same intermittent fault. 

Concorde (F-BTSC) on 25 July 2000: 

The accident of Concorde jet F-BTSC cited, in section 2.6 of report f-sc000725a , that repairs were carried out several times over a period of six weeks and these failed as they were not in accordance with the manufacturer’s specification.  Consequently, a part that detached from a DC10 that took off before Concorde and punctured a tyre that was at the origin of the chain of events.

Lockheed L-1011 (N334EA) on 5 May 1983: 

In report NTSB/AAR-84/04 it was identified that the aircraft had experienced several in-flight engine shutdowns and unscheduled landings prior to the accident.  These had been due to a loss of engine oil and on the day of the accident all 3 engines shutdown simultaneously.  Over a period of 20 months, 12 separate incidents involving O-ring oil seals and master chip detector installation problems were reported  and known at all level of the organisation’s management.  The report cited that the repeated failure of supervisory personnel to require compliance with the prescribed installation procedures, was highlighted as a key factor in the accident. 

Some good practices that you can follow

A lack of control of repetitive defects can lead to hazardous situations. Many of these repetitive defects do not lead systematically to accidents on their own but may increase the risk that system failure could occur at a critical phase of flight. There are number of good practices that should be followed: 

  • Monitor, analyse and investigate recurrent faults through the defect control system by the CAMO.  
  • The maintenance programme should pro-actively monitor reliability and interpret trends to help identify faults that might have an impact on safety.  Check the setting of alert levels, in-service rejection rates or recurrent faults and ensure that an effective investigation takes place to make sure corrective actions are taken. 
  • Temporary measures or trouble shooting, such as resetting computers or swapping components that only clear the fault temporarily should be avoided. 
  • Beware intermittent faults repeatedly signed off without maintenance actions or disregarded or deferred for later rectification – these could lead to a bigger problem in the future if not investigated and rectified effectively. 
  • Report faults correctly in the technical log book and have a clear policy on the management of system faults identified by the aircraft On-board Maintenance System or readouts. 
  • Establish clear policies and coordination between the CAMO, the maintenance organisation and all personnel involved in any maintenance activity.   
  • Take due consideration of instructions and information from the Type Certifacte Holder (TCH) about on the technical concern, such as Airworthiness Directives (ADs), Service Bulletins (SBs) etc. 
  • Components refitted with an EASA Form 1 or equivalent with insufficient trouble shooting and with no records of defects can be a common source of common faults.  Do not re-introduce such equipment into the spares pool with no tracking of malfunctions or suspected defects through workshop reports.
  • The organisational culture should support technical staff with the available resources for effective fault investigations and it should be ensured that operational policies help to manage repetitive recurrent defects on aircraft or components effectively.


Comments (3)

Nuno Aghdassi

Thanks John, very insightful. It's interesting to note that some of these accidents can be attributed to shortcomings in the safety culture of the organisation. They are a manifestation of systemic failures at an organisational level. The last bullet of the 'what you should do' list is thus very pertinent.

Cengiz Turkoglu

Many thanks for highlighting this important issue John.
Last year, I proposed this as a new safety issue at the CAT-CAG and I was pleased that it was accepted. I think this promotion activity is great; however here are some additional considerations.
1. One prominent accident this issue played a contributing factor is the Amsterdam TK1959 accident.
2. In relation to the above accidents, one crucial process which can make a huge difference is the critical interface between engineering/maintenance and flight operations department. To that end, repetitive defects can/should be identified and flight crew should be notified so that they can be prepared if they recur during flight. There used to be an IOSA standard requiring operators to put in place a process to acheive this but unfortunately it was deleted later on.
3. Finally, a risk assessment can be carried out (collaboratively with the CAMO and flight operations) for repetitive defects impacting on safety critical systems such as flight controls, engine controls, autoflight etc. Waiting for reliability programme to deal with such defects could potentially be too late such as in the Amsterdam accident.
My presentation at the CAT-CAG meeting can be accessed @…

Binod Thapa

Many thanks to John for the insightful information and to Cengiz for further describing the issue with the presentation.

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